A sensor unit and a position switch can be used in the private and in the industrial domain. Safety-oriented position switches are used to detect positions of components which move relative to one another. Possible applications are usually oriented toward avoiding or reducing risk. Such a risk might be, by way of example, a health risk or a risk to valuable production means, such as complex machines, expensive raw materials or the like. It is thus conceivable for position switches to be used in safety-oriented applications in buildings engineering, automation engineering or control engineering, for example.
Safety-oriented position switches comprise at least two components of the sensor unit, comprising a sensor, which move independently of one another, and the signal generator. The sensor unit and the signal generator cooperate on the basis of a lock-and-key principle. The sensor unit performs the lock function and the signal generator performs the function of the key, it also being possible for a plurality of signal generators to be used.
In contrast to a mechanical lock-and-key principle, new types of position switches work on a contactless basis. The component sensor unit and signal generator are therefore not mechanically connected to one another, but rather communicate by way of electromagnetic waves.
The application-related level of risk is ascertained using risk analysis. Depending on the level of risk in an application, the application is attributed what is known as a safety integrity level (SIL) based on DIN EN 61508 or a category based on DIN EN 954-1. For the design of the safety-oriented position switch, this means comprehensive measures to protect against failure of the safety-related parts.
Safety-oriented position switches which achieve SIL 3 level according to IEC 61508 or category 4 of DIN EN 954-1 use sensors to pick up redundant measurement signals and supply these signals to two different evaluation units. In this case, the evaluation units can drive a respective actuator; optionally, the two results from the evaluation units may also be logically combined with one another before the actuators are driven.
EP 0 968 567 B1 and DE 103 45 819 A1 disclose safety-oriented contactless position switches which pick up a measurement signal deemed safe, which has normally been encoded a plurality of times, on one channel and supply this measurement signal to two evaluation units. Following the redundant evaluation of the measurement signal, the consistency of the two output signals is checked and evaluated. In this context, the two evaluation units may be capable of communicating with one another during the evaluation. Depending on the result, a trigger signal is then output on two channels.